1. Technical Field
The present invention relates to pyridone-based yellow monoazo dye used in thermal dye transfer in particular, which has good color and durability, and is substituted to imido group.
2. Description of Related Prior Art
In recent years, thermal transfer systems have been used in machinary such as facsimile and copying press. Furthermore it has been developed to obtain prints from pictures which have been generated electronically from a color video camera or computer. According to one way of obtaining such prints, sublimable thermal transfer system has been proposed.
According to thermal transfer system, an electronic picture is first subjected to color separation by color filters. The respective color-separated images are then converted into electrical signal. These signals are then operated on producing Y(Yellow), M(Magenta) and C(Cyan) electrical signals. These signals are then transmitted to a thermal printer.
Transfer sheet applying thermal transferable yellow, magenta and cyan dyes as ink type on sheet-phased substrate is contacted with receiving sheet and then inserted between thermal printing head(TPH) and a platen roller. TPH has many heating elements and is heated up sequentially in response to the yellow, magenta and cyan signals. Transfer sheet is heated selectively according to signal of pattern information corresponding to one color. Dye is transferred to receiving layer from region heated selectively, wherein pattern is formed as form and concentration according to pattern and strength of heat applyed to transfer sheet. The process is then repeated for the other two colors, and then color print corresponding to the original pictures is obtained by combination of three color elements.
Dyes used in sublimable thermal transfer system satisfy some condition. That is, such dyes (1) are sublimated easily and are not decomposed thermally under operating condition of TPH; (2) have a large molar extinction coefficient; (3) have good stability against light, moisture, heat and drug; (4) have good hue at color regeneration; and (5) have simpleness of synthesis.
Dyes used in thermal transfer are disclosed in the following references; U.S. Pat. No. 4,698,651 relates to magenta-dyes having substituted 5-arylazoisothiazole structure.
And U.S. Pat. No. 4,701,439 relates to yellow dyes having cyanovinyl tetrahydro quinoline structure.
U.S. Pat. No. 4,695,287 relates to cyan-dyes having 2-carbamoyl-4-N- (p-substituted monoaryl)-imino!-1,4-naphtoquinone structure.
Also, U.S. Pat. No. 4,764,178 relates to azo dyes having diazoficationable hetero aromatic amines and aromatic coupling components.
Japanese Patent Unexamined Publication No. Soh. 59-78894 relates to cyan-dyes having naphthalendione structure. Japanese Patent Unexamined Publication No. Soh. 59-227948 relates to cyan-dyes having antraquinone structure.
However, dyes described above cannot satisfy the above requirements for thermal transfer system.
Accordingly, dyes with improved color characteristics such as hue, and degree of color development and stability against light and heat are required.
The following reference disclose attempts provide yellow-dyes with the above mentioned improved, U.S. Pat. No. 5,011,813 discloses pyridone-based azo dyes having the following structure; ##STR3## wherein, R.sup.1 is aryl; a substituted or unsubstituted alkoxy alkyl or aryl alkyl group of from 1 to 4 carbon atoms,
R.sup.2 is an alkyl group of from 1 to 12 carbon atoms.
Similarly, European Patent No. 442466 discolses pyridon-based azo dyes having following structure; ##STR4## wherein, R is hydrogen atom, alkyl, cycloalkyl, substituted or unsubstituted phenyl group.
However, yellow dyes of these two pyridone-based azo compounds do not have sufficiently good stability and hue.